A U.S. Air Force reconnaissance plane flying over the Baltic Sea was intercepted by a Russian Su-27 jet in what the U.S. military said Saturday was "an unsafe and unprofessional manner."

The statement from the U.S. European Command said the incident occurred Thursday in international airspace and at no time did the American plane cross into Russian territory. A U.S. military spokesman told CNN that the jet "performed erratic and aggressive maneuvers" as it flew as close as 15 meters to the plane.

Days ago, Russian fighter jets flew very close to the USS Donald Cook in international waters in the Baltic Sea. The crew aboard the warship was dumbfounded to see the apparently unarmed SU-24 planes fly as close as 9 meters from the destroyer — close enough to create a wake in the water.

Russia's Defense Ministry denied the action was provocative, saying the planes were conducting test flights and only observed the Donald Cook before turning away, "in observance of all safety measures."

A Pentagon official described the Russian flights as simulated attack passes. He said sailors on the Donald Cook attempted to reach the Russian planes by radio but got no response.

Some military analysts said they thought the Russian maneuver might have come out of the Kremlin's resentment of U.S. forces operating so close to Russian territory.

NATO has bolstered its military presence in Eastern Europe as a response to the Russian annexation of Crimea in Ukraine in 2014.